The present invention relates to a DC backup power supply system, and more particularly to a DC backup power supply system having a charge-discharge circuit for charging and discharging power between a battery and a DC line.
An uninterruptible power system (UPS) is externally installed on a so-called information processing apparatus such as a server, a router and a storage to deal with an unexpected power failure of a commercial AC power supply system and avoid damages such as data loss to be caused by the power failure. A rack-mount type UPS is commercially available which can be mounted on a rack having a width of about 480 mm called a 19-inch rack for information processing apparatuses. This rack has such a dimension as described, for example, in a “Smart-UPS” catalog of APC Japan, Ltd. This UPS is an AC backup power supply system which supplies an AC output power from a rechargeable battery to a load via an inverter and a transformer to retain the load operation.
Japanese Patent Laid-open Publication JP-A-2000-197347 discloses a DC backup power supply system to be used for a system in which a DC power is supplied from an AC power supply system to a load via an AC/DC converter and a DC/DC converter. In this Publication, it is proposed to connect the DC backup power supply system to an intermediate DC line between both the converters in order to increase the conversion efficiency and reduce the volume and cost.
Although a seal type lead battery generally used as a rechargeable battery of UPS is relatively inexpensive, it has a large volume and is difficult to be mounted on an information processing apparatus or the like. In addition, in order to retain the reliability of an information processing apparatus or the like, double or triple redundancy of a backup power supply system is required so that the size of UPS becomes larger and the mount issue becomes more serious.
Since a seal type lead battery contains lead, it is associated with the problem of adverse affects upon the environments if it is dumped as lead waste.